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Battery cell size detection methodBattery cell size detection method description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20050275369, Battery cell size detection method. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS REFERENCE TO RELATED APPLICATIONS [0001] This application is a continuation-in-part of commonly owned copending U.S. patent application Ser. No. 10/863,920, filed on Jun. 9, 2004, entitled "Multiple Cell Battery Charger Configured with a Parallel Topology", attorney docket no. 211552-00053. BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention relates to a battery charger and more particularly, to a battery charger that is adapted to charge different size battery cells, such as AA and AAA battery cells, in which the battery charger can automatically distinguish between different size battery cells in order to provide the battery cell with the proper charging characteristic. [0004] 2. Description of the Prior Art [0005] Various portable devices and appliances are known to use multiple rechargeable battery cells, such as AA and AAA battery cells. In order to facilitate charging of the battery cells for such multiple cell appliances, multiple cell battery chargers have been developed. Many known battery chargers are configured to receive battery cells having different sizes, such as AA and AAA battery cells. Because the charging characteristics of different size battery cells are different, various mechanical configurations have been developed to sense the size of the battery cell inserted into the charging terminals of the battery charger and properly configure the battery charger for the correct battery cell. [0006] For example, U.S. Pat. Nos. 5,606,238; 6,384,575; and 6,610,941 disclose battery chargers with different mechanical configurations for detecting the size of a battery cell. For example, Rayovac U.S. Pat. No. 5,606,238 discloses a mechanical configuration for sensing the size of a battery cell inserted into the battery charger for charging. A front wall of the battery compartment is formed with a number of apertures sized to coincide with the diameter of various battery cell cathodes. The apertures are located so that when a battery cell is fully inserted within the battery compartment, the cathodes of the cell are received in one of the apertures. The cathode contacts are disposed behind the apertures. The anode in the battery compartment is formed from a leaf spring and is used to bias the battery cell toward the cathode. There are several problems with such a configuration. For example, the mechanical sensing configuration is dependent upon the diameter of the cathode which varies from manufacturer to manufacturer. In addition, the leaf spring may eventually lose its spring tension due to metal fatigue. [0007] U.S. Pat. No. 6,384,575, assigned to Delta Electronics, Inc. of Taiwan, discloses a different type of battery cell mechanical sensing arrangement for a battery charger. This battery charger includes a anode contact and a rotatable cathode contact. When the rotatable cathode contact is in a first position, it is adapted to receive a battery cell of a first longer length. In a second position, the pivotal cathode contact is adapted to receive battery cells of a shorter length. The mechanical sensing arrangement disclosed in the '575 patent requires the user to rotate the rotatable contact before inserting the battery cell in the battery compartment in order to select the appropriate configuration for the battery cell to be charged. Such an operation is cumbersome for the user. [0008] U.S. Pat. No. 6,610,941 discloses another configuration for mechanically sensing the size of the battery cell. This arrangement uses a slide device and a two-prong fork. The configuration disclosed in the '941 patent is used to sense AAA, AA, C, and D-type batteries. The two-prong fork is pivotally mounted. The prongs of the fork are spaced apart at a distance less than the diameter of a type-C battery. The two-prong fork is also rotatably mounted so that when a type-C or D battery is inserted into the battery compartment, a two-prong fork is pushed downwardly. The actuation of the two-prong fork operates a switch which provides an electrical representation of whether type C/D or type AA/AAA batteries have been installed in the battery compartment. The anode is connected to a slider assembly, which, in turn, actuates a switch depending on the length of the battery cell inserted into the battery compartment. Thus, the combination of the two switches can be used to identify the type of battery that has been inserted into the battery compartment. [0009] Such mechanical systems for sensing the size of a battery cell are relatively cumbersome and are subject to wear and are relatively expensive. As such, systems have been developed for electronically determining the size of a battery cell. For example, commonly owned U.S. Pat. Nos. 5,764,030 and 5,998,966 disclose a system for electrically-sensing the battery size and type of smart batteries. Such smart batteries normally include an internal microprocessor that is adapted to communicate with a microprocessor in the battery charger and thus provide data to the battery charger relating to the size of battery cells in the smart battery pack. Unfortunately, the techniques disclosed in the '030 and '966 patents are not suitable for batteries other than smart battery packs. [0010] Fujitsu, U.S. Pat. No. 5,861,729, discloses a battery charger which can electrically distinguish between NiH and NiCd battery based on [FILL IN DETAILS]. Thus there is a need for a battery charger which can effectively and inexpensively distinguish between different size battery cells which are not part of a smart battery pack. SUMMARY OF THE INVENTION [0011] Briefly, the present invention relates to a battery charger that is configured to charge different size battery cells which can automatically determine the size of the battery cell to be charged. The battery charger includes at least one charging circuit and a microprocessor. The charging circuit, in turn, includes a serially connected switching device and a current sensing resistor and a first and second pair of battery terminals that are configured to receive different size battery cells. The first pair of battery terminals is serially connected to a size detection resistor. The serial combination of the first pair of battery terminals and the size detection resistor is connected in parallel with a second pair of battery terminals. The parallel combination is connected in series with the charging circuit. At a nominal charging current, the voltage at the battery terminals will vary by the voltage drop across the size detection resistor. Accordingly, by measuring the voltage at the battery terminals, the system can determine which pair of battery terminals is connected to a battery cell. By configuring the first pair of battery terminals to receive a first battery cell size, for example, size AAA, and serially coupling the first pair of battery terminals to the size detection resistor, and configuring the second pair of battery terminals to receive a second size of battery cell, for example, size AA, the battery cell size can easily be detected electronically by measuring the voltage at the battery terminals. DESCRIPTION OF THE DRAWING [0012] These and other advantages of the present invention will be readily understood with reference to the following specification and attached drawing wherein: [0013] FIG. 1 is a schematic diagram of a battery charger that can electronically sense the size of the battery cell to be charged in accordance with the present invention. [0014] FIG. 2 is an exemplary graphical illustration of the voltage, pressure, and temperature charging characteristics as a function of time for an exemplary NiMH battery. [0015] FIGS. 3A-3E illustrate exemplary flow charts for the battery charger illustrated in FIG. 1. [0016] FIG. 4 is flow chart for a battery charger which illustrates a battery cell size detection method in accordance with the present invention. DETAILED DESCRIPTION [0017] The present invention relates to a multiple cell battery charger configured to charge different size battery cells In accordance with an important aspect of the invention the battery charger is provided with multiple pockets for receiving battery cells having different sizes and can automatically determine the size of the battery cell populated in one of the pockets. [0018] In general, the battery charger 20 includes at least one charging circuit, such as the charging circuit 21 and a microprocessor 26. The charging circuit 21, in turn, includes a switching device Q12, Q13, Q14 and Q15; a serially connected current sensing resistor R37, R45, R53 and R60 and one or more pairs of first and second pair of battery terminals T1,T2 and T3,T4; T5,T6 and T7,T8; T9,TI0 and TI1,T12; T13,T14 and T15,T16, respectively, that are configured to receive different size battery cells, for example size M and AA. Each pair of battery terminals T1,T2 T3,T4; T5,T6; T7,T8; T9,T10; T11,T12; T13,T14; T15,T16, defines a pocket. Each of the first pairs of battery terminals T3,T4; T7,T8; T11,T12; T15,T16, is serially connected to a size detection resistor R1, R2, R3 and R4. The serial combination of the first pair of battery terminals T3,T4; T7,T8; T11,T12; T15,T16 and the size detection resistor R1, R2, R3 and R4 is connected in parallel with the second pair of battery terminals T1,T2; T5,T6; T9,T10; and T13,T14. The parallel combination is connected in series with the charging circuit 21. [0019] At a nominal charging current, for example 750 milliamps, the voltage at the battery terminals will vary by an amount approximately equivalent to the voltage drop across the size detection resistor R1, R2, R3 and R4. Accordingly, by individually measuring the voltage at the nodes N1, N2, N3, and N4, defined by the battery terminals T1,T3; T5,T7; T9,T11; and T13,T15, the system can determine which pair of battery terminals is connected to a battery cell. For example, the first pair of battery terminals may be configured to receive a first battery cell size, for example, size AAA, and configuring the second pair of battery terminals to receive a second size of battery cell, for example, size AA, the nominal voltage of such battery cells is in the range of 1.2-1.5 volts DC. By sizing the size detection resistors R1, R2, R3 and R4 so that at the nominal charging current of, for example, 750 milliamps, the voltage drop across the size detection resistors R1, R2, R3 and R4 is about 0.5 volts DC, measurement of the voltage at the nodes will either be the nominal battery cell voltage of 1.2-1.5 volts if, for example, a AA battery cell is populated in one of the pockets P1, P2, P3 and P4 defined by the second pair of battery terminals T1,T2; T5,T6; T9,T10; and T13,T14. Alternatively, if a, for example, AAA battery cell is populated in one of the pockets P5, P6, P7 and P8 defined by first pair of battery terminals T3,T4; T7,T8; TI1,T12; T15,T16 that are serially connected to one of the size detection resistors R1, R2, R3 and R4, the voltage at the nodes N1, N2, N3, and N4 at a nominal charging current of 750 milliamps will be in the range of 1.7-2.0 volts DC. Thus, the microprocessor 26 can periodically sense the voltage at the nodes N1, N2, N3 and N4 at its port V.sub.sen or alternatively at its port I.sub.s1. Continue reading about Battery cell size detection method... Full patent description for Battery cell size detection method Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Battery cell size detection method patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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